Wikitravel / Wikivoyage é o único site que eu conheço que chega perto. Por exemplo. para Frankfurt diz o seguinte:
If you intend to stay overnight, you may wish to avoid times when trade fairs are held, as this will make finding affordable accommodation a challenging task. The biggest are the Frankfurt Motor Show (Automobil-Ausstellung) every two years in mid-September (next in 2017 and then in 2019) and the Book Fair (Buchmesse) yearly in mid-October
A página Barcelona diz:
Easter week, as well as Christmas to New Year's Eve are very busy times. If you'd rather avoid the crowds, don't come during those dates. Also, avoid visiting during the Mobile World Congress or the Formule 1 racing, unless you are ready to pay extremely expensive hotel rates.
A página Munique diz:
Be aware that the prices can vary significantly by season. Usually you have to pay higher prices during the summer months of June to August. Finding affordable accommodation might be difficult when there are trade fairs in town. Last but not least there is Oktoberfest - around the festival from mid-September to mid-October accommodation prices tend to triple or quadruple and accommodation owners change their terms of use and payment.
Eu não acho que existe uma página global sobre esses eventos, pois manter o controle das datas e dos horários seria bastante difícil. O melhor que você pode conseguir é uma aproximação.